The Safety and SustainabilityFactors of Fume Hoods

Fume hoods are a central component in most laboratories. Whether designing a new laboratory or renovating an existing one, architects are challenged to incorporate safety, reliability and sustainability. These
same issues hold true for laboratory managers
when thinking about updating their existing
equipment. Traditional ducted fume hoods are no
longer the status quo, however. Changes in fume
hood technology now give architects and managers more options when choosing fume hoods.

The most commonly used fume hood type
is the ducted hood and its derivatives. The
ductless fume hood has been used since 1968
with great success for specific, known and predictable chemical handlings. A relatively new
category is the filtered fume hood which, while
lacking a duct, safely retains a broader range

and combination of chemical handlings and
provides superior monitoring, safety alarms
and communication.

Each category of fume hood contributes to
safety, reliability and sustainability in different
ways and to differing levels. New technologies
provide the means of addressing tomorrow’s
laboratory design requirements while safely
reducing initial and operational costs. Furthermore, new technologies can reduce the effort,
complexity and time of designing and constructing laboratories.

Ducted fume hoods

Traditionally, ducted fume hoods have beenconsidered an effective means of protectionfor laboratory personnel. They require fairlystraightforward pre-verification of the chemi-cals intended for use, for example, typical wetchemistry, perchloric acid, acid digestion andradioisotopes. Prior to installation, though,extensive engineering studies are necessaryto determine proper rooftop ventilation andductwork requirements, as well as the make-upair system necessary to compensate for the airconsumed by ducted fume hoods. Since ductedworkstations are tied into the building’s fixedexhaust system, they are rendered immobile.

Reliability is high with ducted fume hoods
and their associated mechanical equipment,
provided that preventative maintenance is
performed on a periodic basis. Complex and
expensive variable air volume (VAV) control
systems are required to enable energy savings
while maintaining user safety.

Ducted fume hoods are large consumers of
energy. Although, with today’s level of sophistication, ducted fume hoods have allowed
for improvements in regard to reducing the
amount of air exhausted into the atmosphere.

Redesigned sash openings, restricted openingsduring use and better containment at lowerface velocities have all contributed to energysavings. However, the consumption of heatedand cooled make-up air is still relatively highand is the driving factor in energy consumptionfor laboratories with higher hood densities. Forexample, a 6-foot hood with the sash verticallyopen 18 inches will exhaust 37,200 cubic feetper hour (cfh) even with a reduced face velocityof 80 feet per minute (fpm). Considering thehigh percentage of fossil fuel used in generatingelectricity, resulting in tons of carbon dioxide, itbecomes clear that a more comprehensive andeffective global solution to achieve green build-ings is necessary.

Ductless fume hoods

A ductless hood is an enclosure fitted with filter
technology designed for specific and dedicated
applications, for example dilution, transfers or
prep work. There is a known, predictable use of
small quantities of chemicals which are easily
reviewed and a filter type is chosen based upon
those chemicals.

Ductless filtering fume hoods have been
around for about 40 years and were inspired
by the activated carbon technology found in
modern gas masks. Ductless fume hoods use
the properties of activated carbon combined
with catalysts and certain neutralizers in order
to filter toxic molecules, therefore, eliminating
their dependency upon HVAC as well as external ductwork. Since no ductwork is required, a
non-ducted filtered hood eliminates the direct
discharge of pollutants into the atmosphere and
therefore contributes to the protection of the
environment. Ductless fume hoods do not consume any air since they filter and recycle purified air back into the laboratory. Furthermore,
ductless hoods do not generate any pollution
linked to energy use, unlike a traditional ducted
fume hood.

The filter selection process should include a
thorough validation review by the manufacturer to determine which specific filter can handle
the application and provide the longest life.